Means for adjusting the impedance of electromagnetic devices



Nov. 4, 1941. c. H. ZIERDT 2,261,323

MEANS FOR ADJUSTING THE IMPEDANCE 0F ELECTROMAGNETIC DEVICES Filed July 26, 1940 Fig.5.

' Conn 2' HIS ATTORNEY Patented Nov. 4, 1941 MEANS FOR ADJUSTING THE IMPEDANCE OF ELECTROMAGNETIC DEVICES Conrad H. Zierdt, Rosedale, Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application July 26, 1940, Serial No. 347,734

2 Claims.

My invention relates to a means for adjusting the impedance characteristics of electromagnetic devices such, for example, as transformers, reactors, impedance bonds, etc.

In railway signaling systems it is frequently essential to the proper operation of the system to be able to cause the transformers, reactors, im-

' pedance bonds, etc. which comprise the system to have a predetermined impedance which can be readily obtained during manufacture, and which will thereafter remain constant throughout the useful life of the device. This is particularly true, for example, of transformers which are employed in coded wayside signaling systems in connection with tuned alternators for supplying alternating current to a track circuit from a source of direct current since the primary winding of such transformers forms a part of a circuit which is tuned to partial resonance at a particular frequency, and the track circuit, in addition to being supplied with alternating current from the transformer secondary winding, is also at times supplied with direct current which flows through this secondary winding and is of sufilcient magnitude that it would cause the primary circuit to become detuned unless the transformer is adjusted to require a high magnetizing current when no direct current is flowing in the secondary winding.

Accordingly, it is the object of my present invention to provide a core structure for use in electromagnetic devices of the type described, which core structure includes means whereby the reluctance of the core can be readily adjusted during manufacture to cause the device to have up of E-sliaped laminations, and in carrying out my invention I construct the E-shaped laminations with a middle leg which is somewhat less than one-half as long as the two outer legs. These laminations are stacked in superposed relation with the legs of adjacent laminations facing in opposite directions, and with a straight lamination of the same width as the middle leg of the E-shaped laminations disposed opposite to each middle leg but separated therefrom by an air gap, the straight laminations each being sufliciently long so that their outer ends pro ject beyond the outer edges of the other laminations. The windings surround the middle leg of the core, and the airgap formed by the ends of the short leg of the E-shaped laminations and the confronting ends of the straight laminations is adjusted to cause the windings to have the desired characteristics by tapping on the outer ends of the straight laminations. whole device is then impregnated with a suitable impregnating compound which thereafter prevents any further movement of the straight laminations relative to the E-shaped laminations, and thus serves as a means for causing the device to permanently retain its proper adjusted characteristics.

According to a modification of my invention, means are provided for simultaneously holding all of the straight laminations at either end of the transformer, and for thereafter locking them in place without the "use of impregnating compound.

It should be particularly pointed out at the outset that while my invention is particularly useful in connection with shell type cores, it can be used on other types of cores as Well.

Other objects and characteristic features of my invention will become apparent as the description proceeds.

I shall describe two forms of electromagnetic devices embodying my invention, and shall then point out the novel features thereof in claims.

In the accompanying drawing, Fig. 1 is a side elevational view showing a transformer constructed in accordance with my invention. Fig. 2 is an end view of the transformer shown in Fig. 1 as it appears when viewed from the right in Fig. 1. Fig. 3 is a transverse sectional view taken substantially on the line III-III of Fig. Figs. 4 and 5 are detail views showing modifications of the transformer illustrated in Figs.

1 and 2.

Similar reference characters refer to similar parts in all five views.

Referring to the drawing, I have here shown my invention applied to a transformer T having a magnetizable core I of the shell type, the central leg of which is surrounded by a primary winding 2, and by one or more secondary windings 3.

According to my invention, the core is made up of E-shaped laminations similar to th lamination la shown in Fig. 3, .which lamination it will be noted has a middle leg which is somewhat less than one-half as long as the two outside legs, and straight laminations similar to the lamination lb shown in Fig. 3, which latter lami- The gap 6 and with its outer end projecting beyond' the outside edges of the E-shaped laminations, as shown in Fig. 3.

With the laminations stacked in this manner, it will be apparent that the middle leg of the core is provided with an air gap formed by the ends of the short legs of the E-shaped laminations and the confronting ends of the straight laminations. It will also be apparent that the reluctance of this air gap can be increased or decreased by sliding the straight laminations toward or away from the associated legs of the E-shaped laminations either individually or in groups, as desired.

The E-shaped laminations are clamped together by means of two U-shaped brackets 4 and 5, and two straight straps la and 5a which are fastened at their ends to the legs of the brackets. The one bracket 4 partly surrounds the core at one side of the windings, and has its upstanding legs disposed in notches formed in the E- shaped laminations, and the other bracket 5 partly surrounds the core at the other side of the windings and has its legs disposed in other notches lc provided in the E-shaped laminations. The straps 4a and 5a may be fastened to the associated brackets in any desired manner, but as here shown the ends of the straps are provided with tongues 4b and 5b which extend through slots in the associated legs of the straps and are then bent upwardly.

The windings 2 and 3 are form-wound and are insulated from each other and from the core by suitable insulation 1 which may, for example, be paper or fiber. The windings are secured to the middle leg of the core i by means of wooden blocks or wedges 8 which are driven between the inside winding and the middle leg of the core on opposite sides of this leg. These blocks also serve to apply a compressive force to the straight laminations of the middle leg which force assists in holding these laminations in place.

As is pointed out hereinbefore, the object of my invention is to cause a transformer of the type described to have predetermined impedance characteristics, and after the laminations of the winding have been assembled and secured in place in the manner thus far described, the transformer is tested to determine its impedance characteristics. If these characteristics do not conform to the desired characteristics, the straight laminations are moved inwardly or outwardly until the desired characteristics are obtained. Ordinarily, the necessary adjustment can be made by moving the straight laminations inwardly, and this result can be accomplished by striking or tapping the outer ends of the straight laminations with a hammer or the like.

After the desired characteristics have been obtained, the whole transformer is impregnated with a suitable impregnating compound such as one of the various asphaltic compounds which are in widespread use. This impregnating compound serves to permanently secure the movable straight laminations in their adjusted positions, thereby insuring that the transformer will retain the desired impedance characteristics throughout its useiul lire.

According to a modified form of my invention, each E-shaped lamination (see Figs. 4 and 5) is provided with a slot I! which is elongated in the direction of the axis of the middle leg, while the straight laminations are provided with a circular hole 12 so disposed that when the laminations are assembled to form the core, the hole in each straight lamination will align vertically with some portion of the slot in the two E-shaped laminations located above and below the straight lamination, respectively. Bolts 0 provided with clamping nuts ID are passed through these aligned holes and slots, and the desired adjustment is made by loosening the nuts on one or the other or both of these bolts and moving the associated straight laminations inwardly or outwardly in a body with the bolt in place. The elongated slots are long enough to give the desired range of adjustment and after the necessary adjustment has been made, the nuts I0 are tightened to clamp the laminations in their adjusted positions.

It should be noted that with the transformer constructed as above described, the windings serve to retain the straight laminations in their proper vertically aligned positions.

If desired, a spacer ll of fiber or the like may be inserted in the air gap of the middle leg to assist in obtaining and maintaining the proper adjustment.

One advantage of the described construction is that it furnishes a rigid structure to hold the impedance adjustment once the necessary adjustment has been made and also causes the air gap to be disposed inside of the winding, thus reducing the tendency to have either the structure influence other apparatus or have a housing of magnetic material in which the structure may be enclosed affect the adjustment of the impedance characteristics. Furthermore, the adjustment of the impedance characteristics is not influenced by the clamping brackets or bolts which may be provided to secure the parts in position.

Another advantage of the described construction is that it provides a convenient and. inexpensive means for obtaining the adjustment during assembly of the transformer.

A further advantage of the described adjustment is that it provides a convenient means for compensating for unavoidable variations in the magnetic characteristics of a core structure.

Although I have herein shown and described only two forms of transformers embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

l. A magnetic core structure for electromagnetic devices comprising a plurality of E-shaped laminations stacked with the legs of alternate laminations extending in opposite directions, each said E-shaped lamination being formed with a middle leg which is less than half as long as the remaining legs, a plurality of straight laminations one disposed opposite the middle leg of each E-shaped lamination to form a continuation thereof but spaced therefrom by an air gap, each said straight lamination being of sufiicient length so that its outer end projects beyond the outer edges of the E-shaped laminations and all of said straight laminations being adjusted to positions to cause said core to have a predeter mined reluctance, and impregnating compound disposed on and about all of said laminations to retain said adjustment.

2. A magnetic core structure for eiectroinagnetic devices comprising a plurality of E-shaped laminations stacked with the legs of alternate laminations extending in opp site directions, each said E-shaped lamination being formed with a middle leg which is less than half as long as the remaining legs, a plurality of straight laminations one disposed opposite the middle leg of each E-shaped lamination to form a continuation thereof but spaced therefrom by an air gap, each said straight lamination being of sufflcient length so that its outer end projects beyond the outer edges of the E-shaped laminations, means for clamping said E-shaped laminations together, elongated slots formed in said E-shaped laminations adjacent the attached ends of their middle legs, holes formed in the straight laminations aligning with said slots, and bolts extending through the aligned holes and slots and serving as a means for adjusting the air gap formed by the free ends of the middle legs of said E-shaped laminations and the con- 15 fronting ends of said straight laminations.

CONRAD H, ZIERDT. 

